The present invention relates generally to hydroforming a workpiece in a die, and, more particularly, to controlling the magnitude of fluid pressure in a workpiece during an automated hydroforming operation.
Hydroforming is a specialized type of die forming process that uses high pressure hydraulic fluid to force a malleable workpiece into contact with the inner surface of a die. Hydroforming is a cost-effective way of shaping metal, such as aluminum, into a product, especially a product having a complex shape. For example, in the automotive industry, hydroforming is used to produce strong, light, rigid unibody structures for vehicles.
To hydroform metal into a vehicle frame rail using an automated process, a hollow, tubular metal workpiece is placed inside a negative die that has the shape of the desired frame rail. Water at high pressure flows into the metal workpiece, and the die is closed around the workpiece. Then the water pressure is increased to a very high magnitude causing the workpiece to expand against the die until it conforms to the shape of the die. The die is then opened, the hydroformed frame rail is removed from the die, and the operation is repeated with another workpiece.
Complex shapes with concavities, which would be difficult or impossible to produce as a standard solid die stamping, can be readily produced by hydroforming. Hydroformed parts can often be made with a higher stiffness to weight ratio and at a lower per unit cost than traditional stamped or stamped and welded parts.
A need exists to control accurately and reliably the fill and form pressure of the water in the workpiece throughout the operation such that the part is pressurized at each stage of the operation with an optimum pressure that varies with the physical properties of the material, the shape and the size of part being formed.